1. Field of the Invention
The invention is directed to a self-pumping hydropneumatic suspension strut.
2. Description of the Related Art
A self-pumping hydropneumatic suspension strut which allows two target level positions to be adjusted is known from DE 10 2008 032 950 B3. To this end, the suspension strut has a first channel between a low-pressure space and a high-pressure space with a first connection orifice and a second channel between these two spaces with a second connection orifice. The two connection orifices are spaced apart axially on a longitudinal axis of a pump rod, which determines the height difference between the two level positions.
The level position provided can be determined via a blocking valve. One parameter can be, for example, the vehicle velocity so as to achieve a lowering of the vehicle, e.g., at higher speeds. On the other hand, it can be provided for a utility vehicle, for example, that lowering the level position is useful for loading or unloading. In sports cars, it is sometimes desirable to raise the vehicle body at low speeds.
However, the unit has limitations with respect to design when the suspension strut has a greater distance from the wheel contact point at a vehicle axle. In this case, a transmission ratio must be taken into account when calculating the required spring force. The transmission ratio describes the length of the wheel lever arm relative to the damper lever arm in a vehicle axle. The transmission ratio, which is generally greater than 1, is squared in the equation for calculating spring force and damping force. This mathematical relationship leads to an extreme pressure increase in the high-pressure space when an appreciable transmission ratio occurs. A comparable problem occurs when large piston rod travel is required.
This effect can be overcome very easily with a conventional helical compression spring, but not with a self-pumping hydropneumatic suspension strut.
It is therefore an object of the present invention to further develop the known suspension strut such that it is usable even with a significant transmission ratio and/or long piston rod travel.